Method and apparatus for selecting carrier for sidelink transmission in wireless communication system

ABSTRACT

A method and apparatus for selecting a carrier for a sidelink communication in a wireless communication system is provided. A user equipment (UE) receives an indication of an aggregated set of carriers among multiple carriers from the network. The aggregated set of carriers may be aggregated based on a destination of the sidelink communication. The UE selects a carrier among the aggregated set of carriers, selects a resource of the selected carrier, and performs the sidelink communication by using the selected resource of the selected carrier.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/KR2018/008360, filed on Jul. 24, 2018,which claims the benefit of U.S. Provisional Application No. 62/536,974,filed on Jul. 25, 2017, the contents of which are all herebyincorporated by reference herein in their entirety.

TECHNICAL FIELD

The present invention relates to wireless communications, and moreparticularly, to a method and apparatus for selecting a carrier forsidelink transmission in a wireless communication system.

BACKGROUND

3rd generation partnership project (3GPP) long-term evolution (LTE) is atechnology for enabling high-speed packet communications. Many schemeshave been proposed for the LTE objective including those that aim toreduce user and provider costs, improve service quality, and expand andimprove coverage and system capacity. The 3GPP LTE requires reduced costper bit, increased service availability, flexible use of a frequencyband, a simple structure, an open interface, and adequate powerconsumption of a terminal as an upper-level requirement.

Work has started in international telecommunication union (ITU) and 3GPPto develop requirements and specifications for new radio (NR) systems.3GPP has to identify and develop the technology components needed forsuccessfully standardizing the new RAT timely satisfying both the urgentmarket needs, and the more long-term requirements set forth by the ITUradio communication sector (ITU-R) international mobiletelecommunications (IMT)-2020 process. Further, the NR should be able touse any spectrum band ranging at least up to 100 GHz that may be madeavailable for wireless communications even in a more distant future.

The NR targets a single technical framework addressing all usagescenarios, requirements and deployment scenarios including enhancedmobile broadband (eMBB), massive machine-type-communications (mMTC),ultra-reliable and low latency communications (URLLC), etc. The NR shallbe inherently forward compatible.

LTE-based vehicle-to-everything (V2X) is urgently desired from marketrequirement as widely deployed LTE-based network provides theopportunity for the vehicle industry to realize the concept of‘connected cars’. The market for vehicle-to-vehicle (V2V) communicationin particular is time sensitive because related activities such asresearch projects, field test, and regulatory work are already ongoingor expected to start in some countries or regions such as US, Europe,Japan, Korea, and China.

3GPP is actively conducting study and specification work on LTE-basedV2X in order to respond to this situation. In LTE-based V2X, PC5-basedV2V has been given highest priority. It is feasible to support V2Vservices based on LTE PC5 interface with necessary enhancements such asLTE sidelink resource allocation, physical layer structure, andsynchronization.

SUMMARY

Carrier aggregation (CA) in sidelink for V2X sidelink communication maybe supported. In this case, a method for selecting a carrier amongaggregated carriers may be required.

In an aspect, a method for selecting a carrier for a sidelinkcommunication by a user equipment (UE) in a wireless communicationsystem is provided. The method includes receiving an indication of anaggregated set of carriers, which is based on a destination of thesidelink communication, among multiple carriers from the network,selecting a carrier among the aggregated set of carriers, selecting aresource of the selected carrier, and performing the sidelinkcommunication by using the selected resource of the selected carrier.

In another aspect, a user equipment (UE) in a wireless communicationsystem is provided. The UE includes a memory, a transceiver, and aprocessor, operably coupled to the memory and the transceiver, thatcontrols the transceiver to receive an indication of an aggregated setof carriers, which is based on a destination of the sidelinkcommunication, among multiple carriers from the network, selects acarrier among the aggregated set of carriers, selects a resource of theselected carrier, and controls the transceiver to perform the sidelinkcommunication by using the selected resource of the selected carrier.

A carrier can be selected among aggregated carriers according to adestination, so that sidelink transmission can be performed on theselected carrier efficiently.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a wireless communication system to whichtechnical features of the present invention can be applied.

FIG. 2 shows another example of a wireless communication system to whichtechnical features of the present invention can be applied.

FIG. 3 shows a block diagram of a user plane protocol stack to whichtechnical features of the present invention can be applied.

FIG. 4 shows a block diagram of a control plane protocol stack to whichtechnical features of the present invention can be applied.

FIG. 5 shows an example of a method for selecting a carrier for sidelinktransmission according to an embodiment of the present invention.

FIG. 6 shows an example of a method for selecting a carrier for sidelinktransmission according to an embodiment of the present invention.

FIG. 7 shows a method for selecting a carrier for a sidelinkcommunication by a UE according to an embodiment of the presentinvention.

FIG. 8 shows a wireless communication system to implement an embodimentof the present invention.

DETAILED DESCRIPTION

The technical features described below may be used by a communicationstandard by the 3rd generation partnership project (3GPP)standardization organization, a communication standard by the instituteof electrical and electronics engineers (IEEE), etc. For example, thecommunication standards by the 3GPP standardization organization includelong-term evolution (LTE) and/or evolution of LTE systems. The evolutionof LTE systems includes LTE-advanced (LTE-A), LTE-A Pro, and/or 5G newradio (NR). The communication standard by the IEEE standardizationorganization includes a wireless local area network (WLAN) system suchas IEEE 802.11a/b/g/n/ac/ax. The above system uses various multipleaccess technologies such as orthogonal frequency division multipleaccess (OFDMA) and/or single carrier frequency division multiple access(SC-FDMA) for downlink (DL) and/or uplink (DL). For example, only OFDMAmay be used for DL and only SC-FDMA may be used for UL. Alternatively,OFDMA and SC-FDMA may be used for DL and/or UL.

FIG. 1 shows an example of a wireless communication system to whichtechnical features of the present invention can be applied.Specifically, FIG. 1 shows a system architecture based on anevolved-UMTS terrestrial radio access network (E-UTRAN). Theaforementioned LTE is a part of an evolved-UTMS (e-UMTS) using theE-UTRAN.

Referring to FIG. 1, the wireless communication system includes one ormore user equipment (UE; 10), an E-UTRAN and an evolved packet core(EPC). The UE 10 refers to a communication equipment carried by a user.The UE 10 may be fixed or mobile. The UE 10 may be referred to asanother terminology, such as a mobile station (MS), a user terminal(UT), a subscriber station (SS), a wireless device, etc.

The E-UTRAN consists of one or more base station (BS) 20. The BS 20provides the E-UTRA user plane and control plane protocol terminationstowards the UE 10. The BS 20 is generally a fixed station thatcommunicates with the UE 10. The BS 20 hosts the functions, such asinter-cell radio resource management (MME), radio bearer (RB) control,connection mobility control, radio admission control, measurementconfiguration/provision, dynamic resource allocation (scheduler), etc.The BS may be referred to as another terminology, such as an evolvedNodeB (eNB), a base transceiver system (BTS), an access point (AP), etc.

A downlink (DL) denotes communication from the BS 20 to the UE 10. Anuplink (UL) denotes communication from the UE 10 to the BS 20. Asidelink (SL) denotes communication between the UEs 10. In the DL, atransmitter may be a part of the BS 20, and a receiver may be a part ofthe UE 10. In the UL, the transmitter may be a part of the UE 10, andthe receiver may be a part of the BS 20. In the SL, the transmitter andreceiver may be a part of the UE 10.

The EPC includes a mobility management entity (MME), a serving gateway(S-GW) and a packet data network (PDN) gateway (P-GW). The MME hosts thefunctions, such as non-access stratum (NAS) security, idle statemobility handling, evolved packet system (EPS) bearer control, etc. TheS-GW hosts the functions, such as mobility anchoring, etc. The S-GW is agateway having an E-UTRAN as an endpoint. For convenience, MME/S-GW 30will be referred to herein simply as a “gateway,” but it is understoodthat this entity includes both the MME and S-GW. The P-GW hosts thefunctions, such as UE Internet protocol (IP) address allocation, packetfiltering, etc. The P-GW is a gateway having a PDN as an endpoint. TheP-GW is connected to an external network.

The UE 10 is connected to the BS 20 by means of the Uu interface. TheUEs 10 are interconnected with each other by means of the PC5 interface.The BSs 20 are interconnected with each other by means of the X2interface. The BSs 20 are also connected by means of the S1 interface tothe EPC, more specifically to the MME by means of the S1-MME interfaceand to the S-GW by means of the S1-U interface. The S1 interfacesupports a many-to-many relation between MMEs/S-GWs and BSs.

FIG. 2 shows another example of a wireless communication system to whichtechnical features of the present invention can be applied.Specifically, FIG. 2 shows a system architecture based on a 5G new radioaccess technology (NR) system. The entity used in the 5G NR system(hereinafter, simply referred to as “NR”) may absorb some or all of thefunctions of the entities introduced in FIG. 1 (e.g. eNB, MME, S-GW).The entity used in the NR system may be identified by the name “NG” fordistinction from the LTE/LTE-A.

Referring to FIG. 2, the wireless communication system includes one ormore UE 11, a next-generation RAN (NG-RAN) and a 5th generation corenetwork (5GC). The NG-RAN consists of at least one NG-RAN node. TheNG-RAN node is an entity corresponding to the BS 10 shown in FIG. 1. TheNG-RAN node consists of at least one gNB 21 and/or at least one ng-eNB22. The gNB 21 provides NR user plane and control plane protocolterminations towards the UE 11. The ng-eNB 22 provides E-UTRA user planeand control plane protocol terminations towards the UE 11.

The 5GC includes an access and mobility management function (AMF), auser plane function (UPF) and a session management function (SMF). TheAMF hosts the functions, such as NAS security, idle state mobilityhandling, etc. The AMF is an entity including the functions of theconventional MME. The UPF hosts the functions, such as mobilityanchoring, protocol data unit (PDU) handling. The UPF an entityincluding the functions of the conventional S-GW. The SMF hosts thefunctions, such as UE IP address allocation, PDU session control.

The gNBs and ng-eNBs are interconnected with each other by means of theXn interface. The gNBs and ng-eNBs are also connected by means of the NGinterfaces to the 5GC, more specifically to the AMF by means of the NG-Cinterface and to the UPF by means of the NG-U interface.

A protocol structure between network entities described above isdescribed. On the system of FIG. 1 and/or FIG. 2, layers of a radiointerface protocol between the UE and the network (e.g. NG-RAN and/orE-UTRAN) may be classified into a first layer (L1), a second layer (L2),and a third layer (L3) based on the lower three layers of the opensystem interconnection (OSI) model that is well-known in thecommunication system.

FIG. 3 shows a block diagram of a user plane protocol stack to whichtechnical features of the present invention can be applied. FIG. 4 showsa block diagram of a control plane protocol stack to which technicalfeatures of the present invention can be applied. The user/control planeprotocol stacks shown in FIG. 3 and FIG. 4 are used in NR. However,user/control plane protocol stacks shown in FIG. 3 and FIG. 4 may beused in LTE/LTE-A without loss of generality, by replacing gNB/AMF witheNB/MME.

Referring to FIG. 3 and FIG. 4, a physical (PHY) layer belonging to L1.The PHY layer offers information transfer services to media accesscontrol (MAC) sublayer and higher layers. The PHY layer offers to theMAC sublayer transport channels. Data between the MAC sublayer and thePHY layer is transferred via the transport channels. Between differentPHY layers, i.e., between a PHY layer of a transmission side and a PHYlayer of a reception side, data is transferred via the physicalchannels.

The MAC sublayer belongs to L2. The main services and functions of theMAC sublayer include mapping between logical channels and transportchannels, multiplexing/de-multiplexing of MAC service data units (SDUs)belonging to one or different logical channels into/from transportblocks (TB) delivered to/from the physical layer on transport channels,scheduling information reporting, error correction through hybridautomatic repeat request (HARQ), priority handling between UEs by meansof dynamic scheduling, priority handling between logical channels of oneUE by means of logical channel prioritization (LCP), etc. The MACsublayer offers to the radio link control (RLC) sublayer logicalchannels.

The RLC sublayer belong to L2. The RLC sublayer supports threetransmission modes, i.e. transparent mode (TM), unacknowledged mode(UM), and acknowledged mode (AM), in order to guarantee various qualityof services (QoS) required by radio bearers. The main services andfunctions of the RLC sublayer depend on the transmission mode. Forexample, the RLC sublayer provides transfer of upper layer PDUs for allthree modes, but provides error correction through ARQ for AM only. InLTE/LTE-A, the RLC sublayer provides concatenation, segmentation andreassembly of RLC SDUs (only for UM and AM data transfer) andre-segmentation of RLC data PDUs (only for AM data transfer). In NR, theRLC sublayer provides segmentation (only for AM and UM) andre-segmentation (only for AM) of RLC SDUs and reassembly of SDU (onlyfor AM and UM). That is, the NR does not support concatenation of RLCSDUs. The RLC sublayer offers to the packet data convergence protocol(PDCP) sublayer RLC channels.

The PDCP sublayer belong to L2. The main services and functions of thePDCP sublayer for the user plane include header compression anddecompression, transfer of user data, duplicate detection, PDCP PDUrouting, retransmission of PDCP SDUs, ciphering and deciphering, etc.The main services and functions of the PDCP sublayer for the controlplane include ciphering and integrity protection, transfer of controlplane data, etc.

The service data adaptation protocol (SDAP) sublayer belong to L2. TheSDAP sublayer is only defined in the user plane. The SDAP sublayer isonly defined for NR. The main services and functions of SDAP include,mapping between a QoS flow and a data radio bearer (DRB), and markingQoS flow ID (QFI) in both DL and UL packets. The SDAP sublayer offers to5GC QoS flows.

A radio resource control (RRC) layer belongs to L3. The RRC layer isonly defined in the control plane. The RRC layer controls radioresources between the UE and the network. To this end, the RRC layerexchanges RRC messages between the UE and the BS. The main services andfunctions of the RRC layer include broadcast of system informationrelated to AS and NAS, paging, establishment, maintenance and release ofan RRC connection between the UE and the network, security functionsincluding key management, establishment, configuration, maintenance andrelease of radio bearers, mobility functions, QoS management functions,UE measurement reporting and control of the reporting, NAS messagetransfer to/from NAS from/to UE.

In other words, the RRC layer controls logical channels, transportchannels, and physical channels in relation to the configuration,reconfiguration, and release of radio bearers. A radio bearer refers toa logical path provided by L1 (PHY layer) and L2 (MAC/RLC/PDCP/SDAPsublayer) for data transmission between a UE and a network. Setting theradio bearer means defining the characteristics of the radio protocollayer and the channel for providing a specific service, and setting eachspecific parameter and operation method. Radio bearer may be dividedinto signaling RB (SRB) and data RB (DRB). The SRB is used as a path fortransmitting RRC messages in the control plane, and the DRB is used as apath for transmitting user data in the user plane.

An RRC state indicates whether an RRC layer of the UE is logicallyconnected to an RRC layer of the E-UTRAN. In LTE/LTE-A, when the RRCconnection is established between the RRC layer of the UE and the RRClayer of the E-UTRAN, the UE is in the RRC connected state(RRC_CONNECTED). Otherwise, the UE is in the RRC idle state (RRC_IDLE).In NR, the RRC inactive state (RRC_INACTIVE) is additionally introduced.RRC_INACTIVE may be used for various purposes. For example, the massivemachine type communications (MMTC) UEs can be efficiently managed inRRC_INACTIVE. When a specific condition is satisfied, transition is madefrom one of the above three states to the other.

A predetermined operation may be performed according to the RRC state.In RRC_IDLE, public land mobile network (PLMN) selection, broadcast ofsystem information (SI), cell re-selection mobility, core network (CN)paging and discontinuous reception (DRX) configured by NAS may beperformed. The UE shall have been allocated an identifier (ID) whichuniquely identifies the UE in a tracking area. No RRC context stored inthe BS.

In RRC_CONNECTED, the UE has an RRC connection with the network (i.e.E-UTRAN/NG-RAN). Network-CN connection (both C/U-planes) is alsoestablished for UE. The UE AS context is stored in the network and theUE. The RAN knows the cell which the UE belongs to. The network cantransmit and/or receive data to/from UE. Network controlled mobilityincluding measurement is also performed.

Most of operations performed in RRC_IDLE may be performed inRRC_INACTIVE. But, instead of CN paging in RRC_IDLE, RAN paging isperformed in RRC_INACTIVE. In other words, in RRC_IDLE, paging formobile terminated (MT) data is initiated by core network and paging areais managed by core network. In RRC_INACTIVE, paging is initiated byNG-RAN, and RAN-based notification area (RNA) is managed by NG-RAN.Further, instead of DRX for CN paging configured by NAS in RRC_IDLE, DRXfor RAN paging is configured by NG-RAN in RRC_INACTIVE. Meanwhile, inRRC_INACTIVE, 5GC-NG-RAN connection (both C/U-planes) is established forUE, and the UE AS context is stored in NG-RAN and the UE. NG-RAN knowsthe RNA which the UE belongs to.

NAS layer is located at the top of the RRC layer. The NAS controlprotocol performs the functions, such as authentication, mobilitymanagement, security control.

The physical channels may be modulated according to 01-DM processing andutilizes time and frequency as radio resources. The physical channelsconsist of a plurality of orthogonal frequency division multiplexing(OFDM) symbols in time domain and a plurality of subcarriers infrequency domain. One subframe consists of a plurality of OFDM symbolsin the time domain. A resource block is a resource allocation unit, andconsists of a plurality of OFDM symbols and a plurality of subcarriers.In addition, each subframe may use specific subcarriers of specific OFDMsymbols (e.g. first OFDM symbol) of the corresponding subframe for aphysical downlink control channel (PDCCH), i.e. L1/L2 control channel. Atransmission time interval (TTI) is a basic unit of time used by ascheduler for resource allocation. The TTI may be defined in units ofone or a plurality of slots, or may be defined in units of mini-slots.

The transport channels are classified according to how and with whatcharacteristics data are transferred over the radio interface. DLtransport channels include a broadcast channel (BCH) used fortransmitting system information, a downlink shared channel (DL-SCH) usedfor transmitting user traffic or control signals, and a paging channel(PCH) used for paging a UE. UL transport channels include an uplinkshared channel (UL-SCH) for transmitting user traffic or control signalsand a random access channel (RACH) normally used for initial access to acell.

Different kinds of data transfer services are offered by MAC sublayer.Each logical channel type is defined by what type of information istransferred. Logical channels are classified into two groups: controlchannels and traffic channels.

Control channels are used for the transfer of control plane informationonly. The control channels include a broadcast control channel (BCCH), apaging control channel (PCCH), a common control channel (CCCH) and adedicated control channel (DCCH). The BCCH is a DL channel forbroadcasting system control information. The PCCH is DL channel thattransfers paging information, system information change notifications.The CCCH is a channel for transmitting control information between UEsand network. This channel is used for UEs having no RRC connection withthe network. The DCCH is a point-to-point bi-directional channel thattransmits dedicated control information between a UE and the network.This channel is used by UEs having an RRC connection.

Traffic channels are used for the transfer of user plane informationonly. The traffic channels include a dedicated traffic channel (DTCH).The DTCH is a point-to-point channel, dedicated to one UE, for thetransfer of user information. The DTCH can exist in both UL and DL.

Regarding mapping between the logical channels and transport channels,in DL, BCCH can be mapped to BCH, BCCH can be mapped to DL-SCH, PCCH canbe mapped to PCH, CCCH can be mapped to DL-SCH, DCCH can be mapped toDL-SCH, and DTCH can be mapped to DL-SCH. In UL, CCCH can be mapped toUL-SCH, DCCH can be mapped to UL-SCH, and DTCH can be mapped to UL-SCH.

Sidelink is described. Sidelink is a UE to UE interface for sidelinkcommunication, vehicle-to-everything (V2X) sidelink communication andsidelink discovery. The Sidelink corresponds to the PC5 interface.Sidelink transmissions are defined for sidelink discovery, sidelinkcommunication and V2X sidelink communication between UEs. The sidelinktransmissions use the same frame structure as the frame structure thatis defined for UL and DL when UEs are in network coverage. However, thesidelink transmission are restricted to a sub-set of the UL resources intime and frequency domain. Various physical channels, transport channelsand logical channels may be defined for sidelink transmission.

Sidelink communication is a mode of communication whereby UEs cancommunicate with each other directly over the PC5 interface. Thiscommunication mode is supported when the UE is served by E-UTRAN andwhen the UE is outside of E-UTRA coverage. Only those UEs authorized tobe used for public safety operation can perform sidelink communication.The terminology “sidelink communication” without “V2X” prefix may onlyconcern public safety unless specifically stated otherwise.

UE performs sidelink communication on subframes defined over theduration of sidelink control (SC) period. The SC period is the periodover which resources allocated in a cell for sidelink controlinformation (SCI) and sidelink data transmissions occur. Within the SCperiod, the UE sends SCI followed by sidelink data. SCI indicates aLayer 1 ID and characteristics of the transmissions (e.g. modulation andcoding scheme (MCS), location of the resource(s) over the duration of SCperiod, timing alignment).

The UE supporting sidelink communication can operate in two modes forresource allocation. The first mode is a scheduled resource allocation,which may be referred to as “Mode 1” for resource allocation of sidelinkcommunication. In the Mode 1, the UE needs to be RRC_CONNECTED in orderto transmit data. The UE requests transmission resources from the BS.The BS schedules transmission resources for transmission of sidelinkcontrol information and sidelink data. The UE sends a scheduling request(dedicated scheduling request (D-SR) or random access) to the BSfollowed by a sidelink buffer status report (BSR). Based on the sidelinkBSR, the BS can determine that the UE has data for a sidelinkcommunication transmission and estimate the resources needed fortransmission. The BS can schedule transmission resources for sidelinkcommunication using configured sidelink radio network temporary identity(SL-RNTI).

The second mode is a UE autonomous resource selection, which may bereferred to as “Mode 2” for resource allocation of sidelinkcommunication. In the Mode 2, a UE on its own selects resources fromresource pools and performs transport format selection to transmitsidelink control information and data. There can be up to 8 transmissionpools either pre-configured for out of coverage operation or provided byRRC signaling for in-coverage operation. Each pool can have one or moreProSe per-packet priority (PPPP) associated with it. For transmission ofa MAC PDU, the UE selects a transmission pool in which one of theassociated PPPP is equal to the PPPP of a logical channel with highestPPPP among the logical channel identified in the MAC PDU. It is up to UEimplementation how the UE selects amongst multiple pools with sameassociated PPPP. There is a one to one association between sidelinkcontrol pool and sidelink data pool. Once the resource pool is selected,the selection is valid for the entire SC period. After the SC period isfinished, the UE may perform resource pool selection again. The UE isallowed to perform multiple transmissions to different destinations in asingle SC period.

A UE in RRC_CONNECTED may send a sidelink UE information message to BSwhen UE becomes interested in sidelink communication. In response, BSmay configure the UE with a SL-RNTI.

A UE is considered in-coverage for sidelink communication whenever itdetects a cell on a public safety ProSe carrier. If the UE is out ofcoverage for sidelink communication, it can only use the Mode 2. If theUE is in coverage for sidelink communication, it may use the Mode 1 orthe Mode 2 as per BS configuration. If the UE is in coverage forsidelink communication, it shall use only the resource allocation modeindicated by BS configuration, unless one of the exceptional casesoccurs. When an exceptional case occurs, the UE is allowed to use theMode 2 temporarily, even though it was configured to use the Mode 1.Resource pool to be used during exceptional case may be provided by BS.

A set of transmission and reception resource pools for SCI when the UEis out of coverage for sidelink communication is pre-configured in theUE. The resource pools for SCI when the UE is in coverage for sidelinkcommunication are configured as follows. The resource pools used forreception are configured by the BS via RRC, in broadcast signaling. Theresource pool used for transmission is configured by the BS via RRC, indedicated or broadcast signaling, if the Mode 2 is used. The resourcepool used for transmission is configured by the BS via RRC, in dedicatedsignaling if the Mode 1 is used. In this case, the BS schedules thespecific resource(s) for SCI transmission within the configuredreception pools.

A set of transmission and reception resource pools for data when the UEis out of coverage for sidelink communication is pre-configured in theUE. The resource pools for data when the UE is in coverage for sidelinkcommunication are configured as follows. The resource pools used fortransmission and reception are configured by the BS via RRC, indedicated or broadcast signaling, if the Mode 2 is used. There is noresource pool for transmission and reception if the Mode 1 is used.

V2X services and V2X sidelink communication is described. V2X servicescan consist of the following four different types, i.e.vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I),vehicle-to-nomadic (V2N) and vehicle-to-pedestrian (V2P). V2X servicescan be provided by PC5 interface and/or Uu interface. Support of V2Xservices via PC5 interface is provided by V2X sidelink communication,which is a mode of communication whereby UEs can communicate with eachother directly over the PC5 interface. This communication mode issupported when the UE is served by E-UTRAN and when the UE is outside ofE-UTRA coverage. Only the UEs authorized to be used for V2X services canperform V2X sidelink communication.

The UE supporting V2X sidelink communication can operate in two modesfor resource allocation. The first mode is a scheduled resourceallocation, which may be referred to as “Mode 3” for resource allocationof V2X sidelink communication. In the Mode 3, the UE needs to beRRC_CONNECTED in order to transmit data. The UE requests transmissionresources from the BS. The BS schedules transmission resources fortransmission of sidelink control information and data. Sidelinksemi-persistent scheduling (SPS) is supported for the Mode 3.

The second mode is a UE autonomous resource selection, which may bereferred to as “Mode 4” for resource allocation of V2X sidelinkcommunication. In the Mode 4, the UE on its own selects resources fromresource pools and performs transport format selection to transmitsidelink control information and data. If mapping between the zones andV2X sidelink transmission resource pools is configured, the UE selectsV2X sidelink resource pool based on the zone UE is located in. The UEperforms sensing for (re)selection of sidelink resources. Based onsensing results, the UE (re)selects some specific sidelink resources andreserves multiple sidelink resources. Up to 2 parallel independentresource reservation processes are allowed to be performed by the UE.The UE is also allowed to perform a single resource selection for itsV2X sidelink transmission.

For V2X sidelink transmission, during handover, transmission resourcepool configurations including exceptional transmission resource pool forthe target cell can be signaled in the handover command to reduce thetransmission interruption. In this way, the UE may use the transmissionsidelink resource pools of the target cell before the handover iscompleted, as long as either synchronization is performed with thetarget cell in case BS is configured as synchronization source orsynchronization is performed with global navigation satellite system(GNSS) in case GNSS is configured as synchronization source. If theexceptional transmission resource pool is included in the handovercommand, the UE starts using randomly selected resources from theexceptional transmission resource pool starting from the reception ofhandover command. If the UE is configured with the Mode 3 in thehandover command, the UE continues to use the exceptional transmissionresource pool while the timer associated with handover is running. Ifthe UE is configured with the Mode 4 in the target cell, the UEcontinues to use the exceptional transmission resource pool until thesensing results on the transmission resource pools for the Mode 4 areavailable. For exceptional cases (e.g. during radio link failure (RLF),during transition from RRC_IDLE to RRC_CONNECTED or during change ofdedicated sidelink resource pools within a cell), the UE may selectresources in the exceptional pool provided in serving cell's SIB21 basedon random selection, and uses them temporarily. During cell reselection,the RRC_IDLE UE may use the randomly selected resources from theexceptional transmission resource pool of the reselected cell until thesensing results on the transmission resource pools for the Mode 4 areavailable.

In order to avoid interruption time in receiving V2X messages due todelay in acquiring reception pools broadcasted from the target cell,synchronization configuration and reception resource pool configurationfor the target cell can be signaled to RRC_CONNECTED UEs in the handovercommand. For RRC_IDLE UE, it is up to UE implementation to minimizesidelink transmission/reception interruption time associated withacquisition of SIB21 of the target cell.

A UE is considered in-coverage on the carrier used for V2X sidelinkcommunication whenever it detects a cell on that carrier. If the UE thatis authorized for V2X sidelink communication is in-coverage for V2Xsidelink communication, it may use the Mode 3 or the Mode 4 as per BSconfiguration. A set of transmission and reception resource pools whenthe UE is out of coverage for V2X sidelink communication may bepre-configured in the UE. V2X sidelink communication resources are notshared with other non-V2X data transmitted over sidelink.

An RRC_CONNECTED UE may send a sidelink UE information message to theserving cell if it is interested in V2X sidelink communicationtransmission in order to request sidelink resources.

If the UE is configured by higher layers to receive V2X sidelinkcommunication and V2X sidelink reception resource pools are provided,the UE receives on those provided resources.

Reception of sidelink V2X communication in different carriers/PLMNs canbe supported by having multiple receiver chains in the UE.

For sidelink SPS, maximum 8 SPS configurations with different parameterscan be configured by BS and all SPS configurations can be active at thesame time. The activation/deactivation of SPS configuration is signalledvia PDCCH by BS. The existing logical channel prioritization based onPPPP is used for sidelink SPS.

UE assistance information can be provided to BS. Reporting of UEassistance information is configured by BS for V2X sidelinkcommunication. The UE assistance information used for V2X sidelinkcommunication includes traffic characteristic parameters (e.g. a set ofpreferred expected SPS interval, timing offset with respect to subframe0 of the system frame number (SFN) 0, PPPP and maximum transport block(TB) size based on observed traffic pattern) related to the SPSconfiguration. The UE assistance information can be reported in caseeither SPS is already configured or not. Triggering of UE assistanceinformation transmission is left to UE implementation. For instance, theUE is allowed to report UE assistance information when change inestimated periodicity and/or timing offset of packet arrival occurs. SRmask per traffic type is not supported for V2X sidelink communication.

For controlling channel utilization, the network is able to indicate howthe UE adapts its transmission parameters for each transmission pooldepending on the channel busy ratio (CBR). The UE measures all theconfigured transmission pools including exceptional pool. Only data poolis measured for the case scheduling assignment (SA) pool and data poolresources are located adjacently, while SA pool and data pool ismeasured separately for the case SA pool and data pool are locatednon-adjacently.

A UE in RRC_CONNECTED can be configured to report CBR measurementresults. For CBR reporting, periodic reporting and event triggeredreporting are supported. Two new reporting events defined only for thedata pool are introduced for event-triggered CBR reporting. CBRevent-triggered reporting is triggered by overloaded threshold and/orless-loaded threshold. The network can configure which of thetransmission pools the UE needs to report.

A UE (regardless of its RRC state) performs transmission parameteradaptation based on the CBR. The exemplary adapted transmissionparameters include maximum transmission power, range of the number ofretransmission per TB, range of physical sidelink shared channel (PSSCH)resource block number, range of MCS, maximum limit on channel occupancyratio. The transmission parameter adaption applies to all transmissionpools including exceptional pool.

Sidelink transmission and/or reception resources including exceptionalpool for different frequencies for the Mode 3 and Mode 4 may beprovided. The sidelink resources for different frequencies can beprovided via dedicated signaling, SIB21 and/or pre-configuration. Theserving cell may indicate to the UE only the frequency on which the UEmay acquire the sidelink resource configuration. If multiple frequenciesand associated resource information are provided, it is up to UEimplementation to select the frequency among the provided frequencies.The UE shall not use pre-configured transmission resource if the UEdetects a cell providing resource configuration or inter-carrierresource configuration for V2X sidelink communication. Frequencies whichmay provide V2X sidelink communication resource configuration orcross-carrier configuration can be pre-configured. The RRC_IDLE UE mayprioritize the frequency that provides resource configuration for V2Xsidelink communication for other carrier during cell reselection.

If the UE supports multiple transmission chains, it may simultaneouslytransmit on multiple carriers via PC5. For the case where multiplefrequencies for V2X are supported, a mapping between service types andV2X frequencies is configured by upper layers. The UE should ensure aservice to be transmitted on the corresponding frequency.

The UE may receive the V2X sidelink communication of other PLMNs. Theserving cell can indicate to the UE the RX resource configuration forinter-PLMN operation directly or only the frequency on which the UE mayacquire the inter-PLMN sidelink resource configuration. Sidelinktransmission in other PLMNs is not allowed.

When UL transmission overlaps in time domain with V2X sidelinktransmission in the same frequency, the UE prioritizes the sidelinktransmission over the UL transmission if the PPPP of sidelink MAC PDU islower than a (pre)configured PPPP threshold. When UL transmissionoverlaps in time domain with sidelink transmission in differentfrequency, the UE may prioritize the sidelink transmission over the ULtransmission or reduce UL transmission power if the PPPP of sidelink MACPDU is lower than a (pre)configured PPPP threshold. However, if ULtransmission is prioritized by upper layer or RACH procedure isperformed, the UE prioritizes UL transmission over any V2X sidelinktransmission (i.e. irrespectively of the sidelink MAC PDU's PPPP).

Detailed operation by MAC sublayer regarding V2X sidelink communicationtransmission is described. In order to transmit on the sidelink sharedchannel (SL-SCH), the MAC entity must have at least one sidelink grant.

Sidelink grants are selected as follows for sidelink communication:

1> if the MAC entity is configured to receive a single sidelink grantdynamically on the PDCCH and more data is available in sidelink trafficchannel (STCH) than can be transmitted in the current SC period, the MACentity shall:

2> using the received sidelink grant determine the set of subframes inwhich transmission of SCI and transmission of first transport blockoccur;

2> consider the received sidelink grant to be a configured sidelinkgrant occurring in those subframes starting at the beginning of thefirst available SC Period which starts at least 4 subframes after thesubframe in which the sidelink grant was received, overwriting apreviously configured sidelink grant occurring in the same SC period, ifavailable;

2> clear the configured sidelink grant at the end of the correspondingSC Period;

1> else, if the MAC entity is configured by upper layers to receivemultiple sidelink grants dynamically on the PDCCH and more data isavailable in STCH than can be transmitted in the current SC period, theMAC entity shall for each received sidelink grant:

2> using the received sidelink grant determine the set of subframes inwhich transmission of SCI and transmission of first transport blockoccur;

2> consider the received sidelink grant to be a configured sidelinkgrant occurring in those subframes starting at the beginning of thefirst available SC Period which starts at least 4 subframes after thesubframe in which the sidelink grant was received, overwriting apreviously configured sidelink grant received in the same subframenumber but in a different radio frame as this configured sidelink grantoccurring in the same SC period, if available;

2> clear the configured sidelink grant at the end of the correspondingSC Period;

1> else, if the MAC entity is configured by upper layers to transmitusing one or multiple pool(s) of resources and more data is available inSTCH than can be transmitted in the current SC period, the MAC entityshall for each sidelink grant to be selected:

2> if configured by upper layers to use a single pool of resources:

3> select that pool of resources for use;

2> else, if configured by upper layers to use multiple pools ofresources:

3> select a pool of resources for use from the pools of resourcesconfigured by upper layers whose associated priority list includes thepriority of the highest priority of the sidelink logical channel in theMAC PDU to be transmitted;

2> randomly select the time and frequency resources for SL-SCH and SCIof a sidelink grant from the selected resource pool. The random functionshall be such that each of the allowed selections can be chosen withequal probability;

2> use the selected sidelink grant to determine the set of subframes inwhich transmission of SCI and transmission of first transport blockoccur;

2> consider the selected sidelink grant to be a configured sidelinkgrant occurring in those subframes starting at the beginning of thefirst available SC Period which starts at least 4 subframes after thesubframe in which the sidelink grant was selected;

2> clear the configured sidelink grant at the end of the correspondingSC Period.

Sidelink grants are selected as follows for V2X sidelink communication:

1> if the MAC entity is configured to receive a sidelink grantdynamically on the PDCCH and data is available in STCH, the MAC entityshall:

2> use the received sidelink grant to determine the number of HARQretransmissions and the set of subframes in which transmission of SCIand SL-SCH occur;

2> consider the received sidelink grant to be a configured sidelinkgrant;

1> else, if the MAC entity is configured by upper layers to transmitbased on sensing using a pool of resources, the MAC entity selects tocreate a configured sidelink grant corresponding to transmissions ofmultiple MAC PDUs, and data is available in STCH, the MAC entity shallfor each Sidelink process configured for multiple transmissions based onsensing:

2> if SL_RESOURCE_RESELECTION_COUNTER=0 and the MAC entity randomlyselects, with equal probability, a value in the interval [0, 1] which isabove the probability configured by upper layers in probResourceKeep; or

2> if the configured sidelink grant cannot accommodate a RLC SDU byusing the maximum allowed MCS configured by upper layers in maxMCS-PSSCHand the MAC entity selects not to segment the RLC SDU; or

2> if a pool of resources is configured or reconfigured by upper layers:

3> clear the configured sidelink grant, if available;

3> randomly select, with equal probability, an integer value in theinterval [5, 15] and set SL_RESOURCE_RESELECTION_COUNTER to the selectedvalue;

3> select the number of HARQ retransmissions from the allowed numbersconfigured by upper layers in allowedRetxNumberPSSCH, and an amount offrequency resources within the range configured by upper layers betweenminRB-NumberPSSCH and maxRB-NumberPSSCH;

3> select one of the allowed values configured by upper layers inrestrictResourceReservationPeriod and set the resource reservationinterval by multiplying 100 with the selected value;

3> randomly select one time and frequency resource from the resourcesindicated by the physical layer. The random function shall be such thateach of the allowed selections can be chosen with equal probability;

3> use the randomly selected resource to select a set of periodicresources spaced by the resource reservation interval for transmissionopportunities of SCI and SL-SCH corresponding to the number oftransmission opportunities of MAC PDUs;

3> if the number of HARQ retransmissions is equal to 1 and there areavailable resources left in the resources indicated by the physicallayer that meet the conditions for more transmission opportunities:

4> randomly select one time and frequency resource from the availableresources. The random function shall be such that each of the allowedselections can be chosen with equal probability;

4> use the randomly selected resource to select a set of periodicresources spaced by the resource reservation interval for the othertransmission opportunities of SCI and SL-SCH corresponding to the numberof retransmission opportunities of the MAC PDUs;

4> consider the first set of transmission opportunities as the newtransmission opportunities and the other set of transmissionopportunities as the retransmission opportunities;

4> consider the set of new transmission opportunities and retransmissionopportunities as the selected sidelink grant.

3> else:

4> consider the set as the selected sidelink grant;

3> use the selected sidelink grant to determine the set of subframes inwhich transmissions of SCI and SL-SCH occur;

3> consider the selected sidelink grant to be a configured sidelinkgrant;

2> else if SL_RESOURCE_RESELECTION_COUNTER=0 and the MAC entity randomlyselects, with equal probability, a value in the interval [0, 1] which isless than or equal to the probability configured by upper layers inprobResourceKeep:

3> clear the configured sidelink grant, if available;

3> randomly select, with equal probability, an integer value in theinterval [5, 15] and set SL_RESOURCE_RESELECTION_COUNTER to the selectedvalue;

3> use the previously selected sidelink grant for the number oftransmissions of the MAC PDUs with the resource reservation interval todetermine the set of subframes in which transmissions of SCI and SL-SCHoccur;

3> consider the selected sidelink grant to be a configured sidelinkgrant;

1> else, if the MAC entity is configured by upper layers to transmitbased on either sensing or random selection using a pool of resources,the MAC entity selects to create a configured sidelink grantcorresponding to transmission(s) of a single MAC PDU, and data isavailable in STCH, the MAC entity shall for a Sidelink process:

2> select the number of HARQ retransmissions from the allowed numbersconfigured by upper layers in allowedRetxNumberPSSCH, and an amount offrequency resources within the range configured by upper layers betweenminRB-NumberPSSCH and maxRB-NumberPSSCH;

2> if transmission based on random selection is configured by upperlayers:

3> randomly select the time and frequency resources for one transmissionopportunity of SCI and SL-SCH from the resource pool. The randomfunction shall be such that each of the allowed selections can be chosenwith equal probability;

2> else:

3> randomly select the time and frequency resources for one transmissionopportunity of SCI and SL-SCH from the resource pool indicated by thephysical layer. The random function shall be such that each of theallowed selections can be chosen with equal probability;

2> if the number of HARQ retransmissions is equal to 1:

3> if transmission based on random selection is configured by upperlayers and there are available resources that meet the conditions forone more transmission opportunity:

4> randomly select the time and frequency resources for the othertransmission opportunity of SCI and SL-SCH corresponding to additionaltransmission of the MAC PDU from the available resources. The randomfunction shall be such that each of the allowed selections can be chosenwith equal probability;

3> else, if transmission based on sensing is configured by upper layersand there are available resources, except the resources already excludedby the physical layer, that meet the conditions for one moretransmission opportunity:

4> randomly select the time and frequency resources for the othertransmission opportunity of SCI and SL-SCH corresponding to additionaltransmission of the MAC PDU from the available resources. The randomfunction shall be such that each of the allowed selections can be chosenwith equal probability;

3> consider a transmission opportunity which comes first in time as thenew transmission opportunity and a transmission opportunity which comeslater in time as the retransmission opportunity;

3> consider both of the transmission opportunities as the selectedsidelink grant;

2> else:

3> consider the transmission opportunity as the selected sidelink grant;

2> use the selected sidelink grant to determine the subframes in whichtransmission(s) of SCI and SL-SCH occur;

2> consider the selected sidelink grant to be a configured sidelinkgrant;

The MAC entity shall for each subframe:

1> if the MAC entity has a configured sidelink grant occurring in thissubframe:

2> if the configured sidelink grant corresponds to transmission of SCI:

3> instruct the physical layer to transmit SCI corresponding to theconfigured sidelink grant;

3> for V2X sidelink communication, deliver the configured sidelink grantand the associated HARQ information to the Sidelink HARQ Entity for thissubframe;

2> else if the configured sidelink grant corresponds to transmission offirst transport block for sidelink communication:

3> deliver the configured sidelink grant and the associated HARQinformation to the Sidelink HARQ Entity for this subframe.

Sidelink communication and V2X sidelink communication related identitiesare described. The following identities are used for sidelinkcommunication and V2X sidelink communication.

(1) Source layer-2 ID (may be referred to as Source ID): The SourceLayer-2 ID identifies the sender of the data in sidelink communicationand V2X sidelink communication. The Source Layer-2 ID is 24 bits longand is used together with Destination Layer-2 ID and logical channel ID(LCID) for identification of the RLC UM entity and PDCP entity in thereceiver.

(2) Destination Layer-2 ID (may be referred to as Destination ID): TheDestination Layer-2 ID identifies the target of the data in sidelinkcommunication and V2X sidelink communication. For sidelinkcommunication, the Destination Layer-2 ID is 24 bits long and is splitin the MAC layer into two bit strings. One bit string is the leastsignificant bit (LSB) part (8 bits) of Destination Layer-2 ID andforwarded to physical layer as Group Destination ID. This identifies thetarget of the intended data in sidelink control information and is usedfor filtering of packets at the physical layer. Second bit string is themost significant bit (MSB) part (16 bits) of the Destination Layer-2 IDand is carried within the MAC header. This is used for filtering ofpackets at the MAC layer. In case of V2X sidelink communication,Destination Layer-2 ID is not split and is carried within the MACheader.

No AS signaling is required for group formation and to configure SourceLayer-2 ID, Destination Layer-2 ID and Group Destination ID in the UE.These identities are either provided by higher layer or derived fromidentities provided by higher layer. In case of groupcast and broadcast,the ProSe UE ID provided by higher layer is used directly as the SourceLayer-2 ID and the ProSe Layer-2 Group ID provided by higher layer isused directly as the Destination Layer-2 ID in the MAC layer. In case ofone-to-one communications, the ProSe UE ID provided by higher layer isused directly as the Source Layer-2 ID or the Destination Layer-2 ID inthe MAC layer. In case of V2X sidelink communication, higher layerprovides Source Layer-2 ID and Destination Layer-2 ID.

SPS is described in detail. As mentioned above, resources allocated bySPS may be used for V2X sidelink communication.

In DL, E-UTRAN can allocate semi-persistent DL resources for the firstHARQ transmissions to UEs. RRC defines the periodicity of thesemi-persistent DL grant. PDCCH indicates whether the DL grant is asemi-persistent one, i.e. whether it can be implicitly reused in thefollowing TTIs according to the periodicity defined by RRC.

When required, retransmissions are explicitly signaled via the PDCCH(s).In the subframes where the UE has semi-persistent DL resource, if the UEcannot find its cell radio network temporary identity (C-RNTI) on thePDCCH(s), a DL transmission according to the semi-persistent allocationthat the UE has been assigned in the TTI is assumed. Otherwise, in thesubframes where the UE has semi-persistent DL resource, if the UE findsits C-RNTI on the PDCCH(s), the PDCCH allocation overrides thesemi-persistent allocation for that TTI and the UE does not decode thesemi-persistent resources.

In UL, E-UTRAN can allocate a semi-persistent UL resource for the firstHARQ transmissions and potentially retransmissions to UEs. RRC definesthe periodicity of the semi-persistent UL grant. PDCCH indicates whetherthe UL grant is a semi-persistent one, i.e. whether it can be implicitlyreused in the following TTIs according to the periodicity defined byRRC.

In the subframes where the UE has semi-persistent UL resource, if the UEcannot find its C-RNTI on the PDCCH(s), a UL transmission according tothe semi-persistent allocation that the UE has been assigned in the TTIcan be made. The network performs decoding of the pre-defined physicalresource blocks (PRBs) according to the pre-defined modulation andcoding scheme (MCS). Otherwise, in the subframes where the UE hassemi-persistent UL resource, if the UE finds its C-RNTI on the PDCCH(s),the PDCCH allocation overrides the persistent allocation for that TTIand the UE's transmission follows the PDCCH allocation, not thesemi-persistent allocation. Retransmissions are either implicitlyallocated in which case the UE uses the semi-persistent UL allocation,or explicitly allocated via PDCCH(s) in which case the UE does notfollow the semi-persistent allocation.

Table 1 shows SPS-Config information element (IE). The IE SPS-Config isused to specify the SPS configuration.

TABLE 1 -- ASN1START SPS-Config ::= SEQUENCE {    semiPersistSchedC-RNTI      C-RNTI    OPTIONAL, -- Need OR    sps-ConfigDL       SPS-ConfigDL   OPTIONAL, -- Need ON    sps-ConfigUL       SPS-ConfigUL    OPTIONAL-- Need ON } SPS-Config-v1430 ::= SEQUENCE {    ul-SPS-V-RNTI-r14         C-RNTI       OPTIONAL,    -- Need OR    sl-SPS-V-RNTI-r14         C-RNTI       OPTIONAL,    -- Need OR   sps-ConfigUL-ToAddModList-r14       SPS-ConfigUL-ToAddModList-r14  OPTIONAL, -- Need ON    sps-ConfigUL-ToReleaseList-r14      SPS-ConfigUL-ToReleaseList- r14  OPTIONAL, -- Need ON   sps-ConfigSL-ToAddModList-r14       SPS-ConfigSL-ToAddModList-r14  OPTIONAL, -- Need ON    sps-ConfigSL-ToReleaseList-r14   SPS-ConfigSL-ToReleaseList-r14    OPTIONAL -- Need ON }SPS-ConfigUL-ToAddModList-r14 ::= SEQUENCE (SIZE (1..maxConfigSPS-r14))OF SPS-ConfigUL SPS-ConfigUL-ToReleaseList-r14 ::= SEQUENCE (SIZE(1..maxConfigSPS-r14)) OF SPS-ConfigIndex-r14SPS-ConfigSL-ToAddModList-r14 ::= SEQUENCE (SIZE (1..maxConfigSPS-r14))OF SPS-ConfigSL-r14 SPS-ConfigSL-ToReleaseList-r14 ::= SEQUENCE (SIZE(1..maxConfigSPS-r14)) OF SPS-ConfigIndex-r14 SPS-ConfigDL::=  CHOICE{   release NULL,    setup SEQUENCE {       semiPersistSchedIntervalDLENUMERATED {    sf10, sf20, sf32, sf40, sf64, sf80,    sf128, sf160,sf320, sf640, spare6,    spare5, spare4, spare3, spare2,    spare1},      numberOfConfSPS-Processes INTEGER (1..8),      n1PUCCH-AN-PersistentList N1PUCCH-AN- PersistentList,       ...,      [[   twoAntennaPortActivated-r10 CHOICE {             release   NULL,             setup    SEQUENCE {               n1PUCCH-AN-PersistentListP1-r10   N1PUCCH-AN-PersistentList             }          } OPTIONAL -- NeedON       ]]    } } SPS-ConfigUL ::=  CHOICE {    release NULL,    setupSEQUENCE {       semiPersistSchedIntervalUL ENUMERATED {    sf10, sf20,sf32, sf40, sf64, sf80,    sf128, sf160, sf320, sf640, sf1-v1430,   sf2-v1430, sf3-v1430, sf4-v1430, sf5-v1430,    spare1},      implicitReleaseAfter ENUMERATED {e2, e3, e4, e8},      p0-Persistent    SEQUENCE {          p0-NominalPUSCH-Persistent   INTEGER (− 126..24),          p0-UE-PUSCH-Persistent    INTEGER(−8..7)       }      OPTIONAL,                    -- Need OP      twoIntervalsConfig    ENUMERATED {true }      OPTIONAL, -- CondTDD       ...,       [[  p0-PersistentSubframeSet2-r12 CHOICE {            release    NULL,             setup    SEQUENCE {               p0-NominalPUSCH-PersistentSubframeSet2-r12       INTEGER(−126..24),                p0-UE-PUSCH-PersistentSubframeSet2-r12         INTEGER (−8..7)             }          }                     OPTIONAL -- Need ON       ]],      [[  numberOfConfU1SPS-Processes-r13    INTEGER(1..8)      OPTIONAL  -- Need OR       ]],      [[  fixedRV-NonAdaptive-r14    ENUMERATED {true}   OPTIONAL,   --Need OR          sps-ConfigIndex-r14   SPS-ConfigIndex-r14     OPTIONAL,   -- Need OR         semiPersistSchedIntervalUL-v1430    ENUMERATED {    sf50,sf100, sf200, sf300, sf400, sf500,    sf600, sf700, sf800, sf900,sf1000, spare5,    spare4, spare3, spare2, spare1} OPTIONAL -- Need OR      ]]    } } SPS-ConfigSL-r14 ::= SEQUENCE {   sps-ConfigIndex-r14           SPS-ConfigIndex-r14,   semiPersistSchedIntervalSL-r14 ENUMERATED { sf20, sf50, sf100, sf200,sf300, sf400, sf500, sf600, sf700, sf800, sf900, sf1000, spare4, spare3,spare2, spare1} } SPS-ConfigIndex-r14 ::= INTEGER (1..maxConfigSPS-r14)N1PUCCH-AN-PersistentList ::= SEQUENCE (SIZE (1..4)) OF INTEGER(0..2047) -- ASN1STOP

A problem of the prior art or a problem to be solved is described.According to the prior art, a resource pool is configured only on asingle carrier. The RRC layer of the UE (hereinafter, simply UE RRC)selects a resource pool on a single carrier. Then, the MAC layer of theUE (hereinafter, simply UE MAC) performs resource (re-)selection on theselected pool, and performs sidelink transmission by using the selectedresource.

It has been discussed to introduce carrier aggregation (CA) in sidelinkfor V2X sidelink communication. CA in sidelink for V2X sidelinkcommunication may apply to both in coverage UEs and out of coverage UEs.In CA in sidelink for V2X sidelink communication, each resource pool(pre)configured for V2X sidelink communication transmission or receptionmay be associated to a single carrier.

If CA in sidelink for V2X sidelink communication is introduced, the UEmay perform parallel transmissions on different carriers. Accordingly,the UE may select multiple carriers independently. In this case,transmitting UEs should configure/select multiple carriers, which causea burden to the transmitting UEs. Further, receiving UEs may need toreceive many carriers, so that the receiving UEs should increasereception capability and power consumption. Accordingly, a method forselecting carriers depending on specific condition may be required.

Hereinafter, a method for selecting sidelink carriers for resource poolsor SPS configurations is described according to embodiments of thepresent invention.

According to an embodiment of the present invention, the networkindicates to the UE which resource pools can be aggregated in sidelinkor which carriers of resource pools can be aggregated in sidelink. Morespecifically, the network may indicate the aggregated carriers to theUE. The aggregated carriers may be indicated per each resource pool, pereach service (e.g. V2V, V2I, V2P), per each frequency band, or per eachband combination. Or, the network may indicate the aggregated resourcepools to the UE. The aggregated resource pools may be indicated per eachservice (e.g. V2V, V2I, V2P), per each frequency band, or per each bandcombination. The network may indicate the aggregated carriers oraggregated resource pools separately for reception and transmission. Thenetwork may indicate the aggregated carriers or aggregated resourcepools via system information and/or a dedicated signaling.

Furthermore, the aggregated carriers or the aggregated resource poolsmay be mapped to an ID, such as Destination ID (e.g. Destination Layer 2ID), Source ID (e.g. Source Layer 2 ID), or UE Identity. The network mayindicate which aggregated carriers or aggregated resource pools aremapped to at least one of Destination ID (e.g. Destination Layer 2 ID),Source ID (e.g. Source Layer 2 ID), or UE Identity. For example, thenetwork may indicate which aggregated carriers or aggregated resourcepools are mapped to a specific destination ID.

According to another embodiment of the present invention, if multipleSPS configurations are used, the network indicates to the UE which SPSconfigurations can be aggregated in sidelink or which carriers of SPSconfigurations can be aggregated in sidelink. More specifically, thenetwork may indicate the aggregated carriers to the UE. The aggregatedcarriers may be indicated per each SPS configuration, per each service(e.g. V2V, V2I, V2P), per each frequency band, or per each bandcombination. Or, the network may indicate the aggregated SPSconfigurations to the UE. The aggregated SPS configurations may beindicated per each service (e.g. V2V, V2I, V2P), per each frequencyband, or per each band combination. The network may indicate theaggregated carriers or aggregated SPS configurations separately forreception and transmission. The network may indicate the aggregatedcarriers or aggregated SPS configurations via system information and/ora dedicated signaling.

Furthermore, the aggregated carriers or the aggregated SPSconfigurations may be mapped to an ID, such as Destination ID (e.g.Destination Layer 2 ID), Source ID (e.g. Source Layer 2 ID), or UEIdentity. The network may indicate which aggregated carriers oraggregated SPS configurations are mapped to one of Destination ID (e.g.Destination Layer 2 ID), Source ID (e.g. Source Layer 2 ID), or UEIdentity. For example, the network may indicate which aggregatedcarriers or aggregated SPS configurations are mapped to a specificdestination ID.

Upon receiving indication of the aggregated carriers for resource poolsor aggregated SPS configurations from the network, the UE selects one ormore carriers for resource pools or one or more SPS configurations,among the indicated aggregated carriers for resource pools or aggregatedSPS configurations. The UE may select one or more carriers for resourcepools or one or more SPS configurations based on one or more of thefollowing aspects.

-   -   UE capability of the UE (e.g. supported band combinations)    -   UE Identity allocated to the UE (e.g. C-RNTI or SAE temporary        mobile subscriber identity (S-TMSI))    -   Source ID allocated to the UE or selected by the UE    -   Destination ID allocated to the UE or selected by the UE    -   Congestion level (e.g. CBR), of the indicated carriers.

The UE selects sidelink resources on the selected carrier(s) forresource pools or the selected SPS configuration(s). For sidelinktransmission, the UE transmits SCI and/or data on the selected sidelinkresources. For sidelink reception, the UE monitors or receives SCI onthe selected carrier(s) for resource pools or the selected SPSconfiguration(s). Then, the UE receives data on the carrier(s) or theSPS configuration(s) indicated by the SCI.

FIG. 5 shows an example of a method for selecting a carrier for sidelinktransmission according to an embodiment of the present invention.

In step S500, the UE receives information on aggregated carriers oraggregated resource pools. The aggregated carriers or aggregatedresource pools may be configured per each service (e.g. V2V, V2I, V2P),per each frequency band, or per each band combination. In addition, theaggregated carriers or aggregated resource pools may be mapped to one ofDestination ID (e.g. Destination Layer 2 ID), Source ID (e.g. SourceLayer 2 ID), or UE Identity. For example, the aggregated carriers oraggregated resource pools may be configured per each Destination ID. Theinformation on the aggregated carriers or aggregated resource pools maybe received via system information and/or a dedicated signaling.

In step S510, the UE selects one or more carriers or one or moreresource pools among the aggregated carriers or aggregated resourcepools. UE RRC may select one or more carriers or one or more resourcepools among the aggregated carriers or aggregated resource pools basedon one or more of the following aspects.

-   -   UE capability of the UE (e.g. supported band combinations)    -   UE Identity allocated to the UE (e.g. C-RNTI or SAE temporary        mobile subscriber identity (S-TMSI))    -   Source ID allocated to the UE or selected by the UE    -   Destination ID allocated to the UE or selected by the UE    -   Congestion level (e.g. CBR), of the indicated carriers.

More specifically, if the network indicates which carriers or resourcepools are mapped to a Destination ID and if the UE is interested in (orallocated/configured with) the Destination ID, the UE may randomlyselect one or more carriers or one or more resource pools mapped to theDestination ID.

Alternatively, if the network indicates N carriers or N resource poolswhich can be aggregated and mapped to a Destination ID and if the UE isallocated or configured with the Destination ID, the UE may select oneor more carriers or one or more resource pools mapped to the DestinationID among N carriers or N resource pools. For example, the selectedcarrier or the selected resource pool may be the i^(th) carrier ori^(th) resource pool in the list of carriers or the list of resourcepools received from the network. The index i may be determined byEquation 1 below.i=Destination ID mod N  [Equation 1]

Alternatively, if the network indicates N carriers or N resource poolswhich can be aggregated and if the UE is allocated or configured withthe Source ID, the UE may select one or more carriers or one or moreresource pools mapped to the Source ID among N carriers or N resourcepools. For example, the selected carrier or the selected resource poolmay be the i^(th) carrier or i^(th) resource pool in the list ofcarriers or the list of resource pools received from the network. Theindex i may be determined by Equation 2 below.i=Source ID mod N  [Equation 2]

Alternatively, if the network indicates N carriers or N resource poolswhich can be aggregated and if the UE is allocated or configured with aUE ID, the UE may select one or more carriers or one or more resourcepools mapped to the UE ID among N carriers or N resource pools. Forexample, the selected carrier or the selected resource pool may be thei^(th) carrier or i^(th) resource pool in the list of carriers or thelist of resource pools received from the network. The index i may bedetermined by Equation 3 below.i=UE ID mod N  [Equation 3]

In step S511, UE RRC informs UE MAC of the selected carriers or theselected resource pools.

In step S520, UE MAC selects sidelink resources on the selectedcarrier(s) or the selected resource pool(s).

In step S530, the UE performs sidelink transmission by using theselected resource. Specifically, the UE may transmit SCI and/or data onthe selected sidelink resources. Furthermore, the UE may monitor orreceive SCI on the selected carrier(s) or the selected resource pool(s),and then, the UE may receive data on the carrier(s) or the resourcepool(s) indicated by the SCI.

FIG. 6 shows an example of a method for selecting a carrier for sidelinktransmission according to an embodiment of the present invention. FIG. 6shows that a resource pool in FIG. 5 is replaced by a SPS configuration.That is, the UE selects one or more carriers of one or more SPSconfigurations, or one or more SPS configurations among the indicatedcarriers or SPS configurations.

In step S600, the UE receives information on aggregated carriers oraggregated SPS configurations. The aggregated carriers or aggregated SPSconfigurations may be configured per each service (e.g. V2V, V2I, V2P),per each frequency band, or per each band combination. In addition, theaggregated carriers or aggregated SPS configurations may be mapped toone of Destination ID (e.g. Destination Layer 2 ID), Source ID (e.g.Source Layer 2 ID), or UE Identity. For example, the aggregated carriersor aggregated SPS configurations may be configured per each DestinationID. The information on the aggregated carriers or aggregated SPSconfigurations may be received via system information and/or a dedicatedsignaling.

In step S610, the UE selects one or more carriers or one or more SPSconfigurations among the aggregated carriers or aggregated SPSconfigurations. UE RRC may select one or more carriers or one or moreSPS configurations among the aggregated carriers or aggregated SPSconfigurations based on one or more of the following aspects.

-   -   UE capability of the UE (e.g. supported band combinations)    -   UE Identity allocated to the UE (e.g. C-RNTI or SAE temporary        mobile subscriber identity (S-TMSI))    -   Source ID allocated to the UE or selected by the UE    -   Destination ID allocated to the UE or selected by the UE    -   Congestion level (e.g. CBR), of the indicated carriers.

More specifically, if the network indicates which carriers or SPSconfigurations are mapped to a Destination ID and if the UE isinterested in (or allocated/configured with) the Destination ID, the UEmay randomly select one or more carriers or one or more SPSconfigurations mapped to the Destination ID.

Alternatively, if the network indicates N carriers or N SPSconfigurations which can be aggregated and mapped to a Destination IDand if the UE is allocated or configured with the Destination ID, the UEmay select one or more carriers or one or more SPS configurations mappedto the Destination ID among N carriers or N SPS configurations. Forexample, the selected carrier or the selected SPS configuration may bethe i^(th) carrier or i^(th) SPS configuration in the list of carriersor the list of SPS configurations received from the network. The index imay be determined by Equation 1 described above.

Alternatively, if the network indicates N carriers or N SPSconfigurations which can be aggregated and if the UE is allocated orconfigured with the Source ID, the UE may select one or more carriers orone or more SPS configurations mapped to the Source ID among N carriersor N SPS configurations. For example, the selected carrier or theselected SPS configuration may be the i^(th) carrier or i^(th) SPSconfiguration in the list of carriers or the list of SPS configurationsreceived from the network. The index i may be determined by Equation 2described above.

Alternatively, if the network indicates N carriers or N SPSconfigurations which can be aggregated and if the UE is allocated orconfigured with a UE ID, the UE may select one or more carriers or oneor more SPS configurations mapped to the UE ID among N carriers or N SPSconfigurations. For example, the selected carrier or the selected SPSconfiguration may be the i^(th) carrier or i^(th) SPS configurations inthe list of carriers or the list of SPS configurations received from thenetwork. The index i may be determined by Equation 3 described above.

In step S611, UE RRC informs UE MAC of the selected carriers or theselected SPS configurations.

In step S620, UE MAC selects sidelink resources on the selectedcarrier(s) or the selected SPS configuration(s), based on a destinationID.

In step S630, the UE performs sidelink transmission by using theselected resource. Specifically, the UE may transmit SCI and/or data onthe selected sidelink resources. Furthermore, the UE may monitor orreceive SCI on the selected carrier(s) or the selected SPSconfiguration(s), and then, the UE may receive data on the carrier(s) orthe SPS configuration(s) indicated by the SCI.

FIG. 7 shows a method for selecting a carrier for a sidelinkcommunication by a UE according to an embodiment of the presentinvention. FIG. 7 assumes that carrier aggregation and/or carrierselection for sidelink communication is performed based on a destinationof sidelink communication. The present invention described above may beapplied to this embodiment.

In step S700, the UE receives an indication of an aggregated set ofcarriers, which is based on a destination of the sidelink communication,among multiple carriers from the network. The aggregated carriers may beconfigured for each resource pool. Or, the aggregated carriers may beconfigured for each SPS configuration. The indication of the aggregatedset of carriers may be received separately for reception andtransmission.

In step S710, the UE selects a carrier among the aggregated set ofcarriers. The carrier may be selected among the aggregated set ofcarriers based on the destination of the sidelink communication. Thedestination of the sidelink communication may be mapped to a DestinationLayer 2 ID. In this case, an index of the carrier may correspond to aresult of a modulo operation of the Destination Layer 2 ID and a numberof carriers in the aggregated set of carriers.

In step S720, the UE selects a resource of the selected carrier. In stepS730, the UE performs the sidelink communication by using the selectedresource of the selected carrier. The performing the sidelinkcommunication may comprise transmitting at least one of SCI or data onthe selected resource of the selected carrier. The performing thesidelink communication may comprise receiving SCI on the selectedresource of the selected carrier, and receiving data on a carrierindicated by the SCI.

FIG. 8 shows a wireless communication system to implement an embodimentof the present invention.

A UE 800 includes a processor 810, a memory 820 and a transceiver 830.The processor 810 may be configured to implement proposed functions,procedures and/or methods described in this description. Layers of theradio interface protocol may be implemented in the processor 810. Thememory 820 is operatively coupled with the processor 810 and stores avariety of information to operate the processor 810. The transceiver 830is operatively coupled with the processor 810, and transmits and/orreceives a radio signal.

A network node 900 includes a processor 910, a memory 920 and atransceiver 930. The processor 910 may be configured to implementproposed functions, procedures and/or methods described in thisdescription. Layers of the radio interface protocol may be implementedin the processor 910. The memory 920 is operatively coupled with theprocessor 910 and stores a variety of information to operate theprocessor 910. The transceiver 930 is operatively coupled with theprocessor 910, and transmits and/or receives a radio signal.

The processors 810, 910 may include application-specific integratedcircuit (ASIC), other chipset, logic circuit and/or data processingdevice. The memories 820, 920 may include read-only memory (ROM), randomaccess memory (RAM), flash memory, memory card, storage medium and/orother storage device. The transceivers 830, 930 may include basebandcircuitry to process radio frequency signals. When the embodiments areimplemented in software, the techniques described herein can beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. The modules can be stored inmemories 820, 920 and executed by processors 810, 910. The memories 820,920 can be implemented within the processors 810, 910 or external to theprocessors 810, 910 in which case those can be communicatively coupledto the processors 810, 910 via various means as is known in the art.

In view of the exemplary systems described herein, methodologies thatmay be implemented in accordance with the disclosed subject matter havebeen described with reference to several flow diagrams. While forpurposed of simplicity, the methodologies are shown and described as aseries of steps or blocks, it is to be understood and appreciated thatthe claimed subject matter is not limited by the order of the steps orblocks, as some steps may occur in different orders or concurrently withother steps from what is depicted and described herein. Moreover, oneskilled in the art would understand that the steps illustrated in theflow diagram are not exclusive and other steps may be included or one ormore of the steps in the example flow diagram may be deleted withoutaffecting the scope of the present disclosure.

What is claimed is:
 1. A method for performing a sidelink communicationby a first user equipment (UE) in a wireless communication system, themethod comprising: receiving system information including information ona first aggregated set of carriers and information on a secondaggregated set of carriers from the network; selecting, by radioresource control (RRC) layer of the first UE, a first carrier among thefirst aggregated set of carriers and a second carrier among the secondaggregated set of carriers; selecting, by medium access control (MAC)layer of the first UE, a first resource of the first carrier and asecond resource of the second carrier; transmitting a first sidelinkcontrol information (SCI) to a second UE through the first resource ofthe first carrier; and receiving a second SCI from a third UE throughthe second resource of the second carrier, wherein the first aggregatedset of carriers is related to a destination of the transmission of thefirst SCI, wherein the second aggregated set of carriers is related to adestination of the reception of the second SCI, wherein the firstcarrier is selected among the first aggregated set of carriers based ona result of a first modulo operation based on a first Destination Layer2 identifier (ID) for the transmission of the first SCI and a number ofcarriers in the first aggregated set of carriers, and wherein the secondcarrier is selected among the second aggregated set of carriers based ona result of a second modulo operation based on a second DestinationLayer 2 ID for the reception of the second SCI and a number of carriersin the second aggregated set of carriers.
 2. The method of claim 1,wherein the first aggregated set of carriers or the second aggregatedset of carriers is configured for each resource pool.
 3. The method ofclaim 1, wherein the first aggregated set of carriers or the secondaggregated set of carriers is configured for each semi-persistentscheduling (SPS) configuration.
 4. The method of claim 1, wherein datarelated to the first SCI is transmitted from the first UE to the secondUE through the first resource.
 5. The method of claim 1, wherein datarelated to the second SCI is transmitted from the third UE to the firstUE through the second resource.
 6. The method of claim 1, wherein thefirst UE is in communication with at least one of a mobile device, anetwork, and/or autonomous vehicles other than the first UE.
 7. Themethod of claim 1, wherein the first carrier is selected based on boththe result of the first modulo operation and channel busy ratio (CBR) ofthe first aggregated set of carriers.
 8. The method of claim 1, whereinthe second carrier is selected based on both the result of the secondmodulo operation and CBR of the second aggregated set of carriers. 9.The method of claim 1, wherein the first carrier is selected based onboth the result of the first modulo operation and a third modulooperation based on a first Source Layer 2 identifier (ID) for thetransmission of the first SCI and the number of carriers in the firstaggregated set of carriers.
 10. The method of claim 1, wherein thesecond carrier is selected based on both the result of the second modulooperation and a fourth modulo operation based on a second Source Layer 2ID for the reception of the second SCI and the number of carriers in thesecond aggregated set of carriers.
 11. A first user equipment (UE)performing sidelink communication in a wireless communication system,the first UE comprising: a memory; a transceiver; and a processor,operably coupled to the memory and the transceiver, that: controls thetransceiver to receive system information including information on afirst aggregated set of carriers and information on a second aggregatedset of carriers from the network; selects, by radio resource control(RRC) layer of the first UE, a first carrier among the first aggregatedset of carriers and a second carrier among the second aggregated set ofcarriers; selects, by medium access control (MAC) layer of the first UE,a first resource of the first carrier and a second resource of thesecond carrier; controls the transceiver to transmit a first sidelinkcontrol information (SCI) to a second UE through the first resource ofthe first carrier; and controls the transceiver to receive a second SCIfrom a third UE through the second resource of the second carrier,wherein the first aggregated set of carriers is related to a destinationof the transmission of the first SCI, wherein the second aggregated setof carriers is related to a destination of the reception of the secondSCI, wherein the first carrier is selected among the first aggregatedset of carriers based on a result of a first modulo operation based on afirst Destination Layer 2 identifier (ID) for the transmission of thefirst SCI and a number of carriers in the first aggregated set ofcarriers, and wherein the second carrier is selected among the secondaggregated set of carriers based on a result of a second modulooperation based on a second Destination Layer 2 ID for the reception ofthe second SCI and a number of carriers in the second aggregated set ofcarriers.
 12. The first UE of claim 11, wherein the first aggregated setof carriers or the second aggregated set of carriers is configured foreach resource pool.
 13. The first UE of claim 11, wherein the firstaggregated set of carriers or the second aggregated set of carriers isconfigured for each semi-persistent scheduling (SPS) configuration.